Zoom lens and imaging apparatus

ABSTRACT

A zoom lens includes: a first lens group having a positive power; a second lens group having a negative power; a third lens group having a positive power; and a fourth lens group having a negative power, in this order from an object side. All of the groups move along an optical axis such that the distance between the first group and the second group gradually becomes greater, the distance between the second group and the third group gradually becomes smaller, and the distance between the third group and the fourth group gradually becomes greater, when changing magnification from a wide angle to a telephoto end. The zoom lens satisfies the conditional formulae: −2.0&lt;fw/f2&lt;−0.8; and −1.0&lt;fw/f4&lt;−0.2, wherein fw is the focal length of the entire system at the wide angle end, f2 is the focal length of the second group, and f4 is the focal length of the fourth group.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/JP2012/003971 filed on Jun.19, 2012, which claims foreign priority to Japanese Application No.2011-138434 filed on Jun. 22, 2011. The entire contents of each of theabove applications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention is related to a zoom lens and an imagingapparatus. Particularly, the present invention is related to a zoom lensa zoom lens having a comparatively short total length, a high angle ofview, and a high variable magnification ratio, and to an imagingapparatus equipped with such a zoom lens.

BACKGROUND ART

Conventionally, zoom lenses having a first lens group having a positiverefractive power, a second lens group having a negative refractivepower, a third lens group having a positive refractive power, and afourth lens group having a negative refractive power, in this order fromthe object side, are known as disclosed in Japanese Unexamined PatentPublication No. 4(1992)-296809, U.S. Pat. No. 6,449,433, and U.S. Pat.No. 7,423,813. Such a configuration is advantageous in shortening thetotal length of a zoom lens, by arranging two lens groups of thetelephoto type.

DISCLOSURE OF THE INVENTION

However, the zoom lenses disclosed in Japanese Unexamined PatentPublication No. 4(1992)-296809, U.S. Pat. No. 6,449,433, and U.S. Pat.No. 7,423,813 have long total lengths, particularly at the telephotoend. In addition, the field of view at the wide angle end isinsufficient, particularly in the zoom lens disclosed in JapaneseUnexamined Patent Publication No. 4(1992)-296809. Further, the variablemagnification ratio is insufficient in the zoom lens disclosed in U.S.Pat. No. 6,449,433. Still further, the field of view at the wide angleend and the variable magnification ratio are both insufficient in thezoom lens disclosed in U.S. Pat. No. 7,423,813.

The present invention has been developed in view of the foregoingcircumstances. It is an object of the present invention to provide azoom lens having a short total length, a sufficiently wide angle ofview, and a high variable magnification ratio.

A zoom lens of the present invention practically comprises:

a first lens group having a positive refractive power;

a second lens group having a negative refractive power;

a third lens group having a positive refractive power; and

a fourth lens group having a negative refractive power, provided in thisorder from an object side;

all of the lens groups moving along an optical axis such that thedistance between the first lens group and the second lens groupgradually becomes greater, the distance between the second lens groupand the third lens group gradually becomes smaller, and the distancebetween the third lens group and the fourth lens group gradually becomesgreater when changing magnification from a wide angle end to a telephotoend; and

the zoom lens satisfies the following conditional formulae:

−2.0<fw/f2<−0.8   (1)

−1.0<fw/f4<−0.2   (2)

wherein fw is the focal length of the entire system at the wide angleend, f2 is the focal length of the second lens group, and f4 is thefocal length of the fourth lens group.

Here, the expression “practically comprises a first lens group . . . asecond lens group . . . a third lens group . . . and a fourth lensgroup” means that the zoom lens may also include lenses that practicallyhave any power, optical elements other than lenses such as aperturestops and cover glass, and mechanical components such as lens flanges, alens barrel, an imaging element, a blur correcting mechanism, etc. Thesame applies to the expression “the fourth lens group practicallycomprises a lens 41 . . . a lens 42 . . . and a lens 43” to be describedlater.

Note that more desirable ranges within the ranges defined in Conditionalformulae (1) and (2) are:

−1.05<fw/f2<−0.85   (1)′

−0.8<fw/f4<−0.5   (2)′.

Note that it is preferable for the zoom lens of the present invention tosatisfy the following conditional formulae:

−2.0<fw/f2<−0.8   (1)

−1.0−fw/f4<−0.2   (2)

wherein fw is the focal length of the entire system at the wide angleend, f2 is the focal length of the second lens group, and f4 is thefocal length of the fourth lens group.

Note that more desirable ranges within the conditions defined byConditional Formulae (1) and (2) are:

−1.05<fw/f2<−0.85   (1)′

−0.8<fw/f4<−0.5   (2)′.

In addition, it is preferable for the zoom lens of the present inventionto satisfy the following conditional formula:

0.6<fw/f3<1.5   (3)

wherein fw is the focal length of the entire system at the wide angleend and f3 is the focal length of the third lens group.

Note that a more desirable range within the conditions defined byConditional Formula (3) is:

0.6<fw/f3<1.0   (3)′.

Further, it is preferable for the zoom lens of the present invention tosatisfy both of the following conditional formulae:

0.10<fw/f1<0.18   (4)

0.10<fw/f3<0.80   (3)″

wherein fw is the focal length of the entire system at the wide angleend, f1 is the focal length of the first lens group, and f3 is the focallength of the third lens group.

In the zoom lens of the present invention, it is desirable for thefourth lens group to practically comprise a lens 41 having a positiverefractive power, a lens 42 having a negative refractive power, and alens 43 having a positive refractive power, provided in this order fromthe object side.

In addition, it is preferable for the lens 42 and the lens 43 to becemented together to form a cemented lens in the zoom lens of thepresent invention.

In the zoom lens of the present invention, it is preferable for the lens42 to be formed by a material having a refractive index higher than therefractive indices of the materials of the lens 41 and the lens 43.

Meanwhile, an imaging apparatus comprises a zoom lens of the presentinvention described above.

The zoom lens according to the present invention practically comprises:the first lens group having a positive refractive power; the second lensgroup having a negative refractive power; the third lens group having apositive refractive power; and the fourth lens group having a negativerefractive power, provided in this order from an object side. That is,two telephoto type lens groups are arranged, and therefore the totallength can be shortened.

In addition, in the zoom lens according to the present invention, all ofthe lens groups move along an optical axis such that the distancebetween the first lens group and the second lens group gradually becomesgreater, the distance between the second lens group and the third lensgroup gradually becomes smaller, and the distance between the third lensgroup and the fourth lens group gradually becomes greater when changingmagnification from a wide angle end to a telephoto end. Therefore,correction of aberrations and amounts of movement by the lens groups canbe appropriately balanced. Thereby, a wide angle of view and a highvariable magnification ratio can be obtained.

Further, the zoom lens of the present invention satisfies both ofConditional Formulae (1) and (2), and therefore the followingadvantageous effects can be obtained. That is, Conditional Formula (1)determines the power distribution of the second lens group with respectto the entire system. If the value of fw/f2 is less than or equal to thelower limit defined in Conditional Formula (1), the refractive power ofthe second lens group will become excessively great, and it will becomedifficult to favorably correct various aberrations. Inversely, if thevalue of fw/f2 is greater than or equal to the upper value defined inConditional Formula (1), the refractive power of the second lens groupwill become excessively small, and it will become difficult to obtain ahigh variable magnification ratio while maintaining a short totallength. Meanwhile, Conditional Formula (2) determines the powerdistribution of the fourth lens group with respect to the entire system.If the value of fw/f4 is less than or equal to the lower limit definedin Conditional Formula (2), the refractive power of the fourth lensgroup will become excessively great, and distortion will increase froman intermediate focal length to the telephoto end. Inversely, if thevalue of fw/f4 is greater than or equal to the upper limit defined inConditional formula (2), the refractive power of the fourth lens groupwill become excessively small, and it will become difficult to obtain ahigh variable magnification ratio while maintaining a short totallength. The above shortcomings can be prevented in the case thatConditional Formulae (1) and (2) are satisfied.

The above advantageous effects will become more prominent in the casethat Conditional Formulae (1)′ and (2)′ are satisfied within the rangesdefined in Conditional Formulae (1) and (2).

In the zoom lens of the present invention, the following advantageouseffects can be obtained particularly in the case that ConditionalFormula (3) is satisfied. That is, Conditional Formula (3) determinesthe power distribution of the third lens group with respect to theentire system. If the value of fw/f3 is less than or equal to the lowerlimit defined in Conditional Formula (3), the refractive power of thethird lens group will become excessively small, and it will becomedifficult to obtain a high variable magnification ratio whilemaintaining a short total length. Inversely, if the value of fw/f3 isgreater than or equal to the upper value defined in Conditional Formula(3), the refractive power of the third lens group will becomeexcessively great, and it will become difficult to favorably correctvarious aberrations. The above shortcomings can be prevented in the casethat Conditional Formula (3) is satisfied.

The above advantageous effects will become more prominent in the casethat Conditional Formula (3)′ is satisfied within the range defined inConditional Formula (3).

In addition, the following advantageous effects can be obtained in thecase that the zoom lens of the present invention satisfies bothConditional Formulae (4) and (3)″. That is, Conditional Formula (4)determines the power distribution of the first lens group with respectto the entire system. If the value of fw/f1 is less than or equal to thelower limit defined in Conditional Formula (4), the refractive power ofthe first lens group becomes excessively small, and it will becomedifficult to obtain a high variable magnification ratio whilemaintaining a short total length. Inversely, if the value of fw/f1 isgreater than or equal to the upper limit defined in Conditional Formula(4), the refractive power of the first lens group will becomeexcessively great, and it will become difficult to favorably correctvarious aberrations. The above shortcomings can be prevented in the casethat Conditional Formula (4) is satisfied. The advantageous effectsobtained by satisfying Conditional Formula (3)″ are basically the sameas those obtained by satisfying Conditional Formulae (3) and (3)′ thatsimilarly determine the range of the value of fw/f3. However, theadvantageous effects become more prominent.

In addition, in the case that the fourth lens group practicallycomprises the lens 41 having a positive refractive power, the lens 42having a negative refractive power, and the lens 43 having a positiverefractive power, provided in this order from the object side, in thezoom lens of the present invention, the refractive power of the fourthlens group can be increased. Therefore, lateral chromatic aberrationsand astigmatic aberrations can be favorably corrected while suppressingthe total length of the zoom lens.

In addition, in the case that the lens 42 and the lens 43 are cementedtogether to constitute a cemented lens in the zoom lens of the presentinvention, peripheral rays causing total reflection can be prevented,while the refractive power of each lens can be increased, which isdesirable.

In the zoom lens of the present invention, the angle of view can bewidened in a simple manner in the case that the lens 42 is formed by amaterial having a higher refractive index than the refractive indices ofthe materials of the lens 41 and the lens 43.

Meanwhile, the imaging apparatus according to the present invention isequipped with the zoom lens of the present invention that exhibits theadvantageous effects described above. Therefore, the lens portion of theimaging apparatus of the present invention can be miniaturized, andimaging with a wide angle of view and a high variable magnificationratio is enabled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional diagram that illustrates the lensconfiguration of a zoom lens according to a first embodiment of thepresent invention.

FIG. 2 is a cross sectional diagram that illustrates the lensconfiguration of a zoom lens according to a second embodiment of thepresent invention.

FIG. 3 is a cross sectional diagram that illustrates the lensconfiguration of a zoom lens according to a third embodiment of thepresent invention.

FIG. 4 is a cross sectional diagram that illustrates the lensconfiguration of a zoom lens according to a fourth embodiment of thepresent invention.

FIG. 5 is a cross sectional diagram that illustrates the lensconfiguration of a zoom lens according to a fifth embodiment of thepresent invention.

FIG. 6 is a cross sectional diagram that illustrates the lensconfiguration of a zoom lens according to a sixth embodiment of thepresent invention.

FIG. 7A through L are diagrams that illustrate various aberrations ofthe zoom lens of the first embodiment.

FIG. 8A through L are diagrams that illustrate various aberrations ofthe zoom lens of the second embodiment.

FIG. 9A through L are diagrams that illustrate various aberrations ofthe zoom lens of the third embodiment.

FIG. 10A through L are diagrams that illustrate various aberrations ofthe zoom lens of the fourth embodiment.

FIG. 11A through L are diagrams that illustrate various aberrations ofthe zoom lens of the fifth embodiment.

FIG. 12A through L are diagrams that illustrate various aberrations ofthe zoom lens of the sixth embodiment.

FIG. 13 is a diagram that schematically illustrates an imaging apparatusaccording to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the attached drawings. FIG. 1 is a crosssectional diagram that illustrates the configuration of a zoom lensaccording to an embodiment of the present invention, and corresponds toa zoom lens of Example 1 to be described later. FIG. 2 through FIG. 6are cross sectional diagrams that illustrate configurations of zoomlenses according to other embodiments of the present invention, andcorresponds to zoom lenses of Examples 2 through 6 to be describedlater. The basic configurations of the embodiments illustrated in FIG. 1through FIG. 11 are the same except that a third lens group G3 isconstituted by two lenses in the embodiment of FIG. 3. The manners inwhich the configurations are illustrated are also the same. Therefore,the zoom lenses according to the embodiments of the present inventionwill be described mainly with reference to FIG. 1. Note that the thirdlens group G3 of the example illustrated in FIG. 3 will be described indetail later.

In FIG. 1, the left side is the object side and the right side is theimage side. A of FIG. 1 illustrates the arrangement of the opticalsystem in a state focused on infinity at the wide angle end (shortestfocal length state). B of FIG. 1 illustrates the arrangement of theoptical system focused on infinity at a position intermediate the wideangle end and the telephoto end. C of FIG. 1 illustrates the arrangementof the optical system in a state focused on infinity a state focused oninfinity at the telephoto end (longest focal length state). The sameapplies to FIGS. 2 through 6 to be described later.

Each of the zoom lenses according to the embodiments of the presentinvention has a first lens group G1 having a positive refractive power,a second lens group G2 having a negative refractive power, a third lensgroup G3 having a positive refractive power, and a fourth lens group G4having a negative refractive power, in this order from the object side.An aperture stop St is included in the third lens group G3. The aperturestop St illustrated in the drawings does not necessarily represent thesize or shape thereof, but only the position thereof on an optical axisZ.

Note that FIG. 1 illustrates an example in which a parallel plateoptical member PP is provided between the fourth lens group G4 and animaging surface Sim. Recent imaging apparatuses employ the 3 CCD format,in which CCD's are employed for each color in order to improve imagequality. In order to be compatible with imaging apparatuses that employthe 3 CCD format, a color separating optical system such as a colorseparating prism may be inserted between the lens system and the imagingsurface Sim. In addition, when the zoom lens is applied to an imagingapparatus, it is preferable for various filters, such as a cover glass,an infrared ray cutoff filter, and a low pass filter, to be providedbetween the optical system and the imaging surface Sim, according to theconfiguration of a camera on which the lens is to be mounted. Theoptical member PP is provided assuming the presence of the cover glass,the various types of filters, and the like.

This zoom lens is configured such that the all of the lens groups, thatis, the first lens group G1 through the fourth lens group G4, move alongthe optical axis Z when changing magnification. More specifically, whenchanging magnification from the wide angel end to the telephoto end, thefirst lens group G1 moves monotonously toward the object side, thesecond lens group G2 moves toward the side of the imaging surface Simalong a curved trajectory, third lens group G3 moves monotonously towardthe object side, the aperture stop St moves integrally with the thirdlens group G3, and the fourth lens group G4 moves toward the object sidealong a curved trajectory. As a result, the distance between the firstlens group G1 and the second lens group G2 gradually becomes greater,the distance between the second lens group G2 and the third lens groupG3 gradually becomes smaller, and the distance between the third lensgroup G3 and the fourth lens group G4 gradually becomes greater.

Note that in FIG. 1, the movement trajectories of the first lens groupG1 through the fourth lens group G4 when changing magnification from thewide angle end to the intermediate position are indicated by the solidarrows between A and B of FIG. 1. In addition, the movement trajectoriesof the first lens group G1 through the fourth lens group G4 whenchanging magnification from the intermediate position to the telephotoend are indicated by the solid arrows between B and C of FIG. 1.However, the movements of the lens groups are not limited to thoseillustrated in FIG. 1. The first lens group G1 and the third lens groupG3 may move along a curved trajectory instead of the monotonousmovement, and the second lens group G2 may move linearly, as long as thedistance between the first lens group and the second lens groupgradually becomes greater, the distance between the second lens groupand the third lens group gradually becomes smaller, and the distancebetween the third lens group and the fourth lens group gradually becomesgreater when changing magnification form the wide angle end to thetelephoto end.

The first lens group G1 is constituted by a first lens L11 having anegative refractive power, a second lens L12 having a positiverefractive power, and a third lens L13 having a positive refractivepower, in this order from the object side. Here, the first lens L11 maybe a negative meniscus lens, the second lens L12 may be a biconvex lens,and the third lens L13 may be a positive meniscus lens, as in theexample illustrated in FIG. 1.

The second lens group G2 is constituted by a fourth lens 21 having anegative refractive power, a fifth lens L22 having a negative refractivepower, and a sixth lens L23 having a positive refractive power, in thisorder from the object side. Here, the fourth lens L21 and the fifth lensL22 may be biconcave lenses, and the sixth lens L23 may be a biconvexlens, as in the example illustrated in FIG. 1.

The third lens group G3 is constituted by a seventh lens L31 having apositive refractive power, an eighth lens L32 having a negativerefractive power, and a ninth lens L33 having a positive refractivepower, in this order from the object side. Here, the seventh lens 31 maybe a biconvex lens, the eighth lens L32 may be a negative meniscus lens,and the ninth lens L33 may be a biconvex lens as in the exampleillustrated in FIG. 1.

The fourth lens group G4 is constituted by a tenth lens L41 having apositive refractive power, an eleventh lens L42 having a negativerefractive power, and a twelfth lens L43 having a positive refractivepower, in this order from the object side. Note that the tenth lens L41,the eleventh lens 42, and the twelfth lens L42 are the previouslydescribed lens 41, lens 42, and lens 43, respectively. Here, the tenthlens L41 may be a biconvex lens, the eleventh lens L42 may be abiconcave lens, and the twelfth lens L43 may be a biconvex lens as inthe example illustrated in FIG. 1.

Note that the eleventh lens L42 and the twelfth lens L43 of the fourthlens group G4 are cemented to each other to constitute a cemented lens.

Note that the embodiment of FIG. 3 is that in which the ninth lens L33is omitted from the third lens group G3, and is the same as theconfiguration described above with respect to the other structures.

The present zoom lens satisfies the conditional formulae:

−2.0<fw/f2<−0.8   (1)

−1.0<fw/f4<−0.2   (2)

wherein fw is the focal length of the entire system at the wide angleend, f2 is the focal length of the second lens group G2, and f4 is thefocal length of the fourth lens group G4.

Note that examples of the numerical values of the embodiments will bedescribed later with reference to Tables 1 through 19. For example, thefocal distance fw of the entire system at the wide angle end of Example1 is shown in the column “Wide Angle End” for item f in Table 2. Thefocal distance fw of the entire system at the wide angle end of Example2 is shown in the same column in Table 5. The same applies to all of theExamples to be described hereinafter.

Table 19 shows the values of fw/f2 and fw/f4, which are related toConditional Formulae (1) and (2), along with the values of fw/f3 andfw/f1, which are related to Conditional Formulae (3) and (4), for eachof the Examples.

As shown in Table 19, the present zoom lens satisfies the followingconditional formulae:

−1.05<fw/f2<−0.85   (1)′

−0.8<fw/f4<−0.5   (2)′

within the ranges defined by Conditional Formulae (1) and (2).

In addition, the present zoom lens satisfies the following conditionalformula:

0.6<fw/f3<1.5   (3)

wherein fw is the focal length of the entire system at the wide angleend and f3 is the focal length of the third lens group G3.

In addition, the present zoom lens satisfies the following conditionalformula:

0.6<fw/f3<1.0   (3)′

within the range defined by Conditional Formula (3).

In addition, the present zoom lens satisfies both of the followingconditional formulae:

0.10<fw/f1<0.18   (4)

0.60<fw/f3<0.80   (3)″

wherein fw is the focal length of the entire system at the wide angleend, f1 is the focal length of the first lens group G1, and f3 is thefocal length of the third lens group G3.

In addition, in the present zoom lens, the eleventh lens L42 is formedby a material having a refractive index higher than the refractiveindices of the materials of the tenth lens L41 and the twelfth lens L43.That is, in Example 1, the refractive indices of the eleventh lens L42,the tenth lens L41, and the twelfth lens L43, are 1.88300, 1.50957, and1.58144, respectively, for example (refer to Table 1 to be describedlater).

Hereinafter, the operational and advantageous effects of the presentzoom lens will be described. First, the present zoom lens comprises: thefirst lens group G1 having a positive refractive power; the second lensgroup G2 having a negative refractive power; the third lens group G3having a positive refractive power; and the fourth lens group G4 havinga negative refractive power, provided in this order from an object side.That is, two telephoto type lens groups are arranged, and therefore thetotal length can be shortened.

In addition, in the present zoom lens, all of the lens groups move alongthe optical axis Z such that the distance between the first lens groupG1 and the second lens group G2 gradually becomes greater, the distancebetween the second lens group G2 and the third lens group G3 graduallybecomes smaller, and the distance between the third lens group G3 andthe fourth lens group G4 gradually becomes greater when changingmagnification from a wide angle end to a telephoto end. Therefore,correction of aberrations and amounts of movement by the lens groups canbe appropriately balanced. Thereby, a wide angle of view and a highvariable magnification ratio can be obtained.

In addition, the present zoom lens satisfies both of ConditionalFormulae (1) and (2). Therefore, the following advantageous effects canbe obtained. That is, Conditional Formula (1) determines the powerdistribution of the second lens group G2 with respect to the entiresystem. If the value of fw/f2 is less than or equal to the lower limitdefined in Conditional Formula (1), the refractive power of the secondlens group G2 will become excessively great, and it will becomedifficult to favorably correct various aberrations. Inversely, if thevalue of fw/f2 is greater than or equal to the upper value defined inConditional Formula (1), the refractive power of the second lens groupG2 will become excessively small, and it will become difficult to obtaina high variable magnification ratio while maintaining a short totallength. Meanwhile, Conditional Formula (2) determines the powerdistribution of the fourth lens group G4 with respect to the entiresystem. If the value of fw/f4 is less than or equal to the lower limitdefined in Conditional Formula (2), the refractive power of the fourthlens group G4 will become excessively great, and distortion willincrease from an intermediate focal length to the telephoto end.Inversely, if the value of fw/f4 is greater than or equal to the upperlimit defined in Conditional formula (2), the refractive power of thefourth lens group G4 will become excessively small, and it will becomedifficult to obtain a high variable magnification ratio whilemaintaining a short total length. The above shortcomings are preventedin the present zoom lens, because Conditional Formulae (1) and (2) aresatisfied.

The above advantageous effects are more prominent in the present zoomlens, because Conditional Formulae (1)′ and (2)′ are satisfied withinthe ranges defined in Conditional Formulae (1) and (2).

The present zoom lens satisfies Conditional Formula (3). Therefore, thefollowing advantageous effects can be obtained. That is, ConditionalFormula (3) determines the power distribution of the third lens group G3with respect to the entire system. If the value of fw/f3 is less than orequal to the lower limit defined in Conditional Formula (3), therefractive power of the third lens group G3 will become excessivelysmall, and it will become difficult to obtain a high variablemagnification ratio while maintaining a short total length. Inversely,if the value of fw/f3 is greater than or equal to the upper valuedefined in Conditional Formula (3), the refractive power of the thirdlens group G3 will become excessively great, and it will becomedifficult to favorably correct various aberrations. The present zoomlens satisfies Conditional Formula (3), and therefore the aboveshortcomings can be prevented.

The above advantageous effects are more prominent in the present zoomlens, because Conditional Formula (3)′ is satisfied within the rangesdefined in Conditional Formula (3).

In addition, the zoom lens of the present invention satisfies both ofConditional Formulae (3)″ and (4). Therefore, the following advantageouseffects can be obtained. That is, Conditional Formula (4) determines thepower distribution of the first lens group G1 with respect to the entiresystem. If the value of fw/f1 is less than or equal to the lower limitdefined in Conditional Formula (4), the refractive power of the firstlens group G1 becomes excessively small, and it will become difficult toobtain a high variable magnification ratio while maintaining a shorttotal length. Inversely, if the value of fw/f1 is greater than or equalto the upper limit defined in Conditional Formula (4), the refractivepower of the first lens group G1 will become excessively great, and itwill become difficult to favorably correct various aberrations. Thepresent lens satisfies Conditional Formula (4), and therefore the aboveshortcomings can be prevented. The advantageous effects obtained bysatisfying Conditional Formula (3)″ are basically the same as thoseobtained by satisfying Conditional Formulae (3) and (3)′ that similarlydetermine the range of the value of fw/f3. However, the advantageouseffects become more prominent.

Further, in the present zoom lens, the fourth lens group G4 comprisesthe tenth lens L41 having a positive refractive power, the eleventh lensL42 having a negative refractive power, and the twelfth lens L43 havinga positive refractive power, provided in this order from the objectside. Therefore, the refractive power of the fourth lens group G4 can beincreased, and lateral chromatic aberrations and astigmatic aberrationscan be favorably corrected while suppressing the total length of thezoom lens.

In addition, the eleventh lens L42 and the twelfth lens L43 of thefourth lens group G4 are cemented together to constitute a cemented lensin the present zoom lens. Therefore, peripheral rays causing totalreflection can be prevented, while the refractive power of each lens canbe increased.

In the zoom lens of the present invention, the angle of view can bewidened in a simple manner, because the eleventh lens L42 is formed by amaterial having a higher refractive index than the refractive indices ofthe materials of the tenth lens L41 and the twelfth lens L43.

Next, examples of the numerical values of the zoom lens of the presentinvention will be described. The cross sections of the lenses of thezoom lenses of Examples 1 through 6 are those illustrated in FIGS. 1through 6, respectively. Regarding the zoom lens of Example 1, basiclens data are shown in Table 1, data related to zoom are shown in Table2, and aspherical surface data are shown in Table 3. Similarly, basiclens data, data related to zoom, and aspherical surface data of the zoomlenses of Examples 2 through 6 are shown in Table 4 through Table 18.Hereinafter, the meanings of the items in the tables will be describedfor those related to Example 1. The same applies to the tables relatedto Examples 2 through 6.

In the basic lens data of Table 1, ith (i=1, 2, 3, . . . ) lens surfacenumbers that sequentially increase from the object side to the imageside, with the lens surface at the most object side designated as first,are shown in the column Si. The radii of curvature of ith surfaces areshown in the column Ri, the distances between an ith surface and ani+1st surface along the optical axis Z are shown in the column Ri. Notethat the signs of the radii of curvature are positive in cases that thesurface shape is convex toward the object side, and negative in casesthat the surface shape is convex toward the image side.

In the basic lens data, the item Ndj represents the refractive index ofthe jth (j=1, 2, 3, . . . ) constituent element that sequentiallyincreases from the object side to the image side, with the lens at themost object side designated as first, with respect to the d line(wavelength: 587.6 nm). The item vdj represents the Abbe's number of thejth constituent element with respect to the d line. Note that theaperture stop St is also included in the basic lens data, and the radiusof curvature of the surface corresponding to the aperture stop St isshown as “∞” (aperture stop).

D5, D10, D16, and D21 in the basic lens data of Table 1 are thedistances between surfaces that change when changing magnification. D5is the distance between the first lens group G1 and the second lensgroup G2, D10 is the distance between the second lens group G2 and thethird lens group G3, D16 is the distance between the third lens group G3and the fourth lens group G4, and D21 is the distance between the fourthlens group G4 and the optical member PP. Note that in Table 7 that showsdata for Example 3, D14 is the distance between the third lens group G3and the fourth lens group G4, and D19 is the distance between the fourthlens group G4 and the optical member PP. In addition, Bf represents backfocus.

The data of Table 2 related to zoom shows values of the focal length(f), the F value (Fno.), and the full angle of view (2ω) of the entiresystem and the distances (D5, D10, D16, and D21) among surfaces thatchange when changing magnification at the wide angle end, at theintermediate position, and at the telephoto end. Note that in Table 8that shows data for Example 3, the distances among surfaces that changewhen changing magnification are shown as D5, D10, D14, and D19.

In the lens data of Table 1, surface numbers of aspherical surfaces aredenoted with the mark “*”, and radii of curvature of paraxial regionsare shown as the radii of curvature of the aspherical surfaces. Theaspherical surface data of Table 3 show the surface numbers of theaspherical surfaces, and the aspherical surface coefficients related toeach of the aspherical surfaces. In the numerical values of theaspherical surface data of Table 3, “E-n (n: integer)” means “−10^(−n)”.Note that the aspherical surface coefficients are the values of thecoefficients K and Am (m=3, 4, 5, . . . , 12) in the aspherical surfaceformula below:

Zd=C·h ²/{1+(1−K·C ² ·h ²)^(1/2) }+ΣAm·h ^(m)

wherein: Zd is the depth of the aspherical surface (the length of anormal line that extends from a point on the aspherical surface having aheight h to a plane perpendicular to the optical axis that contacts thepeak of the aspherical surface), h is the height (the distance from theoptical axis to the surface of the lens), C is the inverse of theparaxial radius of curvature, and A and Am are aspherical surfacecoefficients (m=1, 2, 3, . . . , 12).

The tables below show numerical values which are rounded off at apredetermined number of digits. In addition, degrees are used as theunits for angles and mm are used as the units for lengths in the data ofthe tables below. However, it is possible for optical systems to beproportionately enlarged or proportionately reduced and utilized.Therefore, other appropriate units may be used.

TABLE 1 Example 1: Basic Lens Data Si Ri Ndj νdj (Surface (Radius of Di(Refractive (Abbe's Number) Curvature) (Distance) Index) Number) 182.574161 1.000 2.00069 25.46 2 33.851722 3.500 1.59240 68.40 3−58.107266 0.100 4 20.719807 2.500 1.59240 68.40 5 69.281040 D5  6−70.871893 0.600 1.88300 40.80 7 6.821939 2.000 8 −27.934254 0.6001.88300 40.80 9 6.279334 2.200 1.84666 23.78 10 −54.898934 D10 115.604211 2.200 1.51680 64.20 12 −11.702347 0.600 2.00069 25.46 13−57.724423 0.200 *14 12.320857 1.000 1.50957 56.36 *15 −17.201229 1.07016 ∞ (Aperture Stop) D16 *17 20.871946 1.600 1.50957 56.36 *18 −5.9966540.400 19 −3.508368 0.600 1.88300 40.80 20 5.502244 1.600 1.58144 40.8921 −9.893763 D21 22 ∞ 0.900 1.51680 64.20 23 ∞ 2.500 (Bf) *AsphericalSurface

TABLE 2 Example 1: Data Related to Zoom Item Wide Angle End IntermediatePosition Telephoto End f 5.661 17.903 56.614 Fno. 2.83 4.54 5.91 2ω 70.425.2 8.08 D5 1.000 8.985 16.623 D10 14.726 7.235 0.800 D16 3.112 3.4565.566 D21 1.000 5.887 6.897

TABLE 3 Example 1: Aspherical Surface Coefficients Surface Number 14 1517 18 K 1.0000 1.0000 1.0000 1.0000 A3 −2.0689E−03 — — −7.4573E−03 A4 3.8147E−03 −1.6570E−03 −2.2611E−03  1.0013E−02 A5 −9.2052E−03 — —−2.4553E−02 A6  7.7691E−03 −3.7118E−05 −7.4913E−04  3.7743E−02 A7−4.0019E−03 — — −4.3187E−02 A8  1.2109E−03 −4.9440E−06   2.9531E−04 2.8636E−02 A9 −2.0417E−04 — — −9.6849E−03 A10  1.4526E−05 −1.2738E−08−5.0926E−05  1.2812E−03

TABLE 4 Example 2: Basic Lens Data Si Ri Ndj νdj (Surface (Radius of Di(Refractive (Abbe's Number) Curvature) (Distance) Index) Number) 174.523984 1.000 2.00069 25.46 2 33.050228 3.500 1.59240 68.40 3−62.707217 0.100 4 20.270980 2.500 1.59240 68.40 5 58.159046 D5  6−82.092241 0.600 1.88300 40.80 7 6.736333 2.000 8 −26.721744 0.6001.88300 40.80 9 6.437753 2.200 1.84666 23.78 10 −48.074437 D10 115.551186 2.200 1.51680 64.20 12 −11.596110 0.600 2.00069 25.46 13−57.062529 0.200 *14 13.187360 1.000 1.50957 56.36 *15 −16.278102 1.06816 ∞ D16 (Aperture Stop) *17 14.196261 1.600 1.50957 56.36 *18 −7.4420670.400 19 −3.619089 0.600 1.88300 40.80 20 5.397045 1.600 1.58144 40.8921 −9.878848 D21 22 ∞ 0.900 1.51680 64.20 23 ∞ 2.500 (Bf) *AsphericalSurface

TABLE 5 Example 2: Data Related to Zoom Item Wide Angle End IntermediatePosition Telephoto End f 5.582 17.653 55.824 Fno. 3.08 4.48 5.83 2ω 71.225.6 8.2 D5 1.000 9.285 17.341 D10 14.860 7.208 0.800 D16 2.976 3.3225.200 D21 1.000 5.706 6.545

TABLE 6 Example 2: Aspherical Surface Coefficients Surface Number 14 1517 18 K 1.0000 1.0000 1.0000 1.0000 A4 −2.6711E−03 −2.0109E−03−1.8826E−03 −4.6163E−03 A6 −8.0942E−05 −5.3296E−05 −4.0225E−04−6.7027E−04 A8 −9.8763E−06 −6.1076E−06 1.6106E−04 2.5131E−04 A102.4835E−08 −1.4527E−08 −2.3690E−05 −4.0598E−05

TABLE 7 Example 3: Basic Lens Data Si Ri Ndj νdj (Surface (Radius of Di(Refractive (Abbe's Number) Curvature) (Distance) Index) Number) 169.481090 1.000 2.00069 25.46 2 32.569060 3.500 1.59240 68.40 3−64.765941 0.100 4 19.794520 2.500 1.59240 68.40 5 55.026576 D5  6−98.921349 0.600 1.88300 40.80 7 6.932365 2.690 8 −24.865861 0.6001.88300 40.80 9 6.542884 2.200 1.84666 23.78 10  −50.294642 D10 11*5.035184 2.200 1.49700 81.36 12  −6.706341 0.700 2.00069 25.46 13 −9.319617 1.102 14  ∞ D14 (Aperture Stop) 15* 9.142787 1.600 1.5095756.36 16* −6.59822 0.400 17  −3.543152 0.600 1.88300 40.80 18  5.8002751.500 1.58144 40.89 19  −14.648650 D19 20  ∞ 0.900 1.51680 64.20 21  ∞3.000 (Bf) *Aspherical Surface

TABLE 8 Example 3: Data Related to Zoom Item Wide Angle End IntermediatePosition Telephoto End f 5.593 17.687 55.932 Fno. 3.08 4.49 5.84 2ω 71.225.4 8.18 D5 1.000 9.965 17.015 D10 14.597 7.158 0.800 D14 3.120 3.4304.878 D19 1.092 5.166 7.149

TABLE 9 Example 3: Aspherical Surface Coefficients Surface Number 11 1516 K 1.0000 1.0000 1.0000 A4 −1.0071E−03 −7.7010E−05 −2.4944E−03 A6−1.7854E−05 −4.4050E−04 −9.7573E−04 A8 −1.5312E−06 1.8921E−04 4.2773E−04A10 3.7732E−08 −2.2850E−05 −6.0655E−05

TABLE 10 Example 4: Basic Lens Data Si Ri Ndj νdj (Surface (Radius of Di(Refractive (Abbe's Number) Curvature) (Distance) Index) Number) 173.028405 1.000 2.00069 25.46 2 33.121364 3.500 1.59240 68.40 3−62.361005 0.100 4 20.071570 2.500 1.59240 68.40 5 59.348820 D5  6−75.253036 0.600 1.88300 40.80 7 6.680597 2.071 8 −25.061533 0.6001.88300 40.80 9 6.061330 2.200 1.84666 23.78 10 −56.426907 D10 115.861177 2.200 1.51680 64.20 12 −9.626489 0.600 2.00069 25.46 13−28.796869 0.200 *14 20.860609 1.000 1.50957 56.36 *15 −12.991012 1.88316 ∞ D16 (Aperture Stop) *17 19.664396 1.600 1.50957 56.36 *18 −6.7436630.400 19 −3.569211 0.600 1.88300 40.80 20 6.069590 1.600 1.59551 39.2221 −8.822736 D21 22 ∞ 0.900 1.51680 64.20 23 ∞ 2.500 (Bf) *AsphericalSurface

TABLE 11 Example 4: Data Related to Zoom Item Wide Angle EndIntermediate Position Telephoto End f 5.700 18.025 57.000 Fno. 3.14 4.575.95 2ω 70.2 25.0 8.02 D5 1.000 9.483 17.190 D10 14.051 7.069 0.800 D162.858 3.243 5.645 D21 1.000 5.791 5.967

TABLE 12 Example 4: Aspherical Surface Coefficients Surface Number 14 1517 18 K 1.0000 1.0000 1.0000 1.0000 A4 −2.7283E−03 −2.1122E−03−2.7233E−03 −5.7286E−03 A6 −1.3714E−04 −9.7241E−05 −2.7323E−04−4.1494E−04 A8 1.0859E−06 1.5598E−06 1.3839E−04 1.8439E−04 A10−6.7908E−07 −4.9997E−07 −2.7859E−05 −3.6551E−05

TABLE 13 Example 5: Basic Lens Data Si Ri Ndj νdj (Surface (Radius of Di(Refractive (Abbe's Number) Curvature) (Distance) Index) Number) 171.869450 1.000 2.00069 25.46 2 32.948799 3.500 1.59240 68.40 3−68.211814 0.100 4 20.559494 2.500 1.59240 68.40 5 56.240868 D5  6−79.805880 0.600 1.81600 46.57 7 6.302445 2.000 8 −34.357275 0.6001.88300 40.80 9 6.186877 2.200 1.84666 23.78 10 −142.743023 D10 115.149811 2.200 1.51823 58.96 12 −8.212405 0.600 2.00069 25.46 13−27.729317 0.200 *14 19.570955 1.000 1.50957 56.36 *15 −10.367415 0.80016 ∞ D16 (Aperture Stop) *17 138.106936 1.600 1.50957 56.36 *18−5.657980 0.400 19 −3.311469 0.600 1.88300 40.80 20 5.778462 1.6001.61293 36.96 21 −9.492001 D21 22 ∞ 0.900 1.51680 64.20 23 ∞ 2.500 (Bf)*Aspherical Surface

TABLE 14 Example 5: Data Related to Zoom Wide Angle IntermediateTelephoto Item End Position End f 5.689 17.989 56.886 Fno. 3.14 4.565.94 2ω 70.2 25.0 8.04 D5 1.000 10.255 18.519 D10 13.676 6.945 0.800 D162.939 3.245 4.941 D21 1.000 5.466 6.011

TABLE 15 Example 5: Aspherical Surface Coefficients Surface Number 14 1517 18 K 1.0000 1.0000 1.0000 1.0000 A4 −3.8405E−03 −2.8694E−03−2.9115E−03 −5.2690E−03 A6 −1.3958E−04 −7.2667E−05 −5.0751E−04−7.2145E−04 A8 −7.6842E−06 −4.8401E−06 2.5973E−04 3.0111E−04 A10−4.9320E−07 −3.8090E−07 −4.5429E−05 −5.2736E−05

TABLE 16 Example 6: Basic Lens Data Si Ri Ndj νdj (Surface (Radius of Di(Refractive (Abbe's Number) Curvature) (Distance) Index) Number) 183.622488 1.000 2.00069 25.46 2 36.494800 3.500 1.59240 68.40 3−62.182033 0.100 4 21.281442 2.500 1.59240 68.40 5 58.121861 D5  6−85.099880 0.600 1.81600 46.57 7 7.314359 2.002 8 −27.081750 0.6001.88300 40.80 9 5.882316 2.200 1.80518 25.46 10 −36.680210 D10 115.909209 2.200 1.51823 58.96 12 −7.654065 0.600 2.00069 25.46 13−15.150038 0.200 *14 29.784986 1.000 1.50957 56.36 *15 −15.391312 0.80216 ∞ D16 (Aperture Stop) *17 10.456710 1.600 1.50957 56.36 *18 −8.4938690.400 19 −3.969446 0.600 1.88300 40.80 20 3.952503 1.600 1.59551 39.2221 −15.028599 D21 22 ∞ 0.900 1.51680 64.20 23 ∞ 2.500 (Bf) *AsphericalSurface

TABLE 17 Example 6: Data Related to Zoom Wide Angle IntermediateTelephoto Item End Position End f 5.326 16.842 53.260 Fno. 2.936 4.9285.958 2ω 73.8 26.8 8.6 D5 1.000 8.309 17.969 D10 15.885 7.172 0.800 D162.786 3.153 4.832 D21 1.000 6.029 6.626

TABLE 18 Example 6: Aspherical Surface Coefficients Surface Number 14 1517 18 K 1.0000 1.0000 1.0000 1.0000 A4 −3.8405E−03 −2.8694E−03−2.9115E−03 −5.2690E−03 A6 −1.3958E−04 −7.2667E−05 −5.0751E−04−7.2145E−04 A8 −7.6842E−06 −4.8401E−06 2.5973E−04 3.0111E−04 A10−4.9320E−07 −3.8090E−07 −4.5429E−05 −5.2736E−05

Table 19 shows values corresponding to Conditional Formulae (1) through(4) of the zoom lenses of Examples 1 through 6. The values in Table 19are related to the d line.

TABLE 19 Values Related to Conditional Formulae Exam- Exam- Exam- Exam-Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 (1) fw/f2 −0.944 −0.919−0.925 −0.994 −0.977 −0.832 (2) fw/f4 −0.638 −0.612 −0.555 −0.568 −0.744−0.641 (3) fw/f3 0.726 0.715 0.699 0.715 0.792 0.690 (4) fw/f1 0.1740.167 0.171 0.176 0.165 0.151

The spherical aberration, the astigmatic aberration, the distortion, andthe lateral chromatic aberration of the zoom lens of Example 1 at thewide angle end are illustrated in A through D of FIG. 7, respectively.The spherical aberration, the astigmatic aberration, the distortion, andthe lateral chromatic aberration of the zoom lens of Example 1 at theintermediate position are illustrated in E through H of FIG. 7,respectively. The spherical aberration, the astigmatic aberration, thedistortion, and the lateral chromatic aberration of the zoom lens ofExample 1 at the telephoto end are illustrated in I through L of FIG. 7,respectively.

Each of the diagrams that illustrate the aberrations use the d line(wavelength: 587.6 nm) as a standard. However, in the diagrams thatillustrate spherical aberration, aberrations related to wavelengths of460.0 nm and 615.0 nm are also shown. In addition, the diagrams thatillustrate lateral chromatic aberration also show aberrations related towavelengths of 460.0 nm and 615.0 nm. In the diagrams that illustrateastigmatic aberrations, aberrations in the sagittal direction areindicated by solid lines, while aberrations in the tangential directionare indicated by broken lines. In the diagrams that illustrate sphericalaberrations, “Fno.” denotes F values. In the other diagrams thatillustrate the aberrations, ω denotes half angles of view.

Similarly, the aberrations of the zoom lens of Example 2 are illustratedin A through L of FIG. 8. In addition, the aberrations of the zoomlenses of Examples 3 through 11 are illustrated in FIG. 9 through FIG.12.

Note that FIG. 1 illustrates an example in which the optical member PPis provided between the lens system and the imaging surface.Alternatively, various filters such as low pass filters and filters thatcut off specific wavelength bands may be provided among each of thelenses. As a further alternative, coatings that have the same functionsas the various filters may be administered on the surfaces of thelenses.

Next, an imaging apparatus according to an embodiment of the presentinvention will be described. FIG. 13 is a diagram that schematicallyillustrates an imaging apparatus 10 according to the embodiment of thepresent invention that employs the zoom lens 1 of the embodiment of thepresent invention. The imaging apparatus may be a surveillance camera, avideo camera, an electronic still camera, or the like.

The imaging apparatus 10 illustrated in FIG. 13 is equipped with: thezoom lens 1; a filter 2 provided toward the image side of the zoom lens1; an imaging element 3 that captures images of subjects focused by thezoom lens 1; a signal processing section 4 that processes signals outputfrom the imaging element 2; a magnification control section 5 thatchanges the magnification of the zoom lens 1; and a focus controlsection 6 that performs focus adjustments.

The zoom lens 1 comprises the first lens group G1 having a positiverefractive power, the second lens group G2 having the negativerefractive power, the third lens group G3 having the positive refractivepower, and the fourth lens group G4 having the negative refractivepower. In the zoom lens 1, all of the lens group move along the opticalaxis Z when changing magnification from the wide angle end to thetelephoto end such that the distance between the first lens group G1 andthe second lens group G2 gradually becomes greater, the distance betweenthe second lens group G2 and the third lens group G3 gradually becomessmaller, and the distance between the third lens group G3 and the fourthlens group G4 gradually becomes greater. Note that the lens groups areschematically illustrated in FIG. 13.

The imaging element 3 captures an optical image formed by the zoom lens1 and outputs electrical signals. The imaging surface thereof isprovided to match the imaging plane of the zoom lens 1. A CCD, a CMOS,or the like may be employed as the imaging element 3.

The imaging apparatus is equipped with the zoom lens 1 according to thepresent invention. Therefore, the lens portion thereof can beminiaturized, and imaging becomes possible with a wide angle of view anda high variable magnification ratio.

Note that although not illustrated in FIG. 13, the imaging apparatus 10may be further equipped with a blur correcting mechanism that moves alens having a positive refractive power that constitutes a portion ofthe second lens group G3 or the entire third lens group G3 in adirection perpendicular to the optical axis Z in order to correctblurring of obtained images due to vibration or shaky hands. Inaddition, the lens group to be moved is not limited to the third lensgroup. The entirety or a portion of another lens group may be moved in adirection perpendicular to the optical axis Z to correct blurring ofobtained images due to vibration or shaky hands. As a furtheralternative, the imaging element 3 may be moved instead of a lens.

The present invention has been described with reference to theembodiments and Examples thereof. However, the present invention is notlimited to the embodiments and Examples described above, and variousmodifications are possible. For example, the values of the radii ofcurvature, the distances among surfaces, the refractive indices, theAbbe's numbers, the aspherical surface coefficients, etc., are notlimited to the numerical values indicated in connection with theExamples, and may be other values.

What is claimed is:
 1. A zoom lens, practically comprising: a first lensgroup having a positive refractive power; a second lens group having anegative refractive power; a third lens group having a positiverefractive power; and a fourth lens group having a negative refractivepower, provided in this order from an object side; all of the lensgroups moving along an optical axis such that the distance between thefirst lens group and the second lens group gradually becomes greater,the distance between the second lens group and the third lens groupgradually becomes smaller, and the distance between the third lens groupand the fourth lens group gradually becomes greater when changingmagnification from a wide angle end to a telephoto end; and the zoomlens satisfies at least one of the following conditional formulae:−1.05<fw/f2<−0.85   (1)′−0.8<fw/f4<−0.5   (2)′ wherein fw is the focal length of the entiresystem at the wide angle end, f2 is the focal length of the second lensgroup, and f4 is the focal length of the fourth lens group.
 2. A zoomlens as defined in claim 1, wherein: the fourth lens group practicallycomprises a lens 41 having a positive refractive power, a lens 42 havinga negative refractive power, and a lens 43 having a positive refractivepower, provided in this order from the object side.
 3. A zoom lens asdefined in claim 2, wherein: the lens 42 and the lens 43 are cementedtogether.
 4. A zoom lens as defined in claim 2, wherein: the refractiveindex of the lens 42 is higher than the refractive indices of the lens41 and the lens
 43. 5. A zoom lens as defined in claim 3, wherein: therefractive index of the lens 42 is higher than the refractive indices ofthe lens 41 and the lens
 43. 6. An imaging apparatus comprising a zoomlens as defined in claim 1.